Milling system and method under different lubrication conditions

ABSTRACT

The disclosure provides a method and system for milling injected cutting fluid under different working conditions. By analyzing influence of airflow fields in a milling area under different working conditions on injection of cutting fluid, an influence rule of a helical angle and a rotation speed of a cutter on the flow field is quantitatively analyzed, an optimal target distance of a nozzle, an angle between the nozzle and a milling cutter feeding direction and an angle between the nozzle and the surface of a workpiece are comprehensively determined, the nozzle is set according to a determined setting manner, and lubricating oil is sprayed to the milling area by utilizing the nozzle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.201811401223.3 with a filing date of Nov. 22, 2018. The content of theaforementioned applications, including any intervening amendmentsthereto, are incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to a method and system for milling injectedcutting fluid under different working conditions.

BACKGROUND OF THE PRESENT INVENTION

The statement of this part only provides background technicalinformation related to the present disclosure, and does not necessarilyconstitute the existing technology.

At present, milling is the most commonly used cutting in mechanicalmanufacturing industry, which is high in processing and productionefficiency, wide in processing target distance and high in processingprecision. However, when in milling, the contact time between a cutterand a workpiece is extremely short, the sharp friction occurs betweenthe rake face of the cutter and the chips and between the flank face ofthe cutter and the workpiece so that a large number of cutting heat isgenerated, the cutter is sharply abraded, cutter failure is too fast,and the improvement of the processing efficiency is seriouslyrestricted. Therefore, cooling liquid is very important in processing,which has the functions of lubrication, cooling, cleaning, rustprevention and the like.

The conventional milling causes huge damage on environment and workersdue to use of a large amount of cutting fluid. In order to protect theenvironment and reduce the cost, micro lubrication and nano fluid microlubrication technologies have more advantages. However, this fluidsupply method has certain disadvantages that the air has viscidity, themilling cutter rotating at high speed can affect the hydrodynamiccharacteristics of an air flow field close to the milling cutter, theair around the milling cutter is originally static, but the millingcutter rotating at high speed can cause air to flow, and the closer theair is to the cutting edge, the higher the flow speed of air is, thusforming a closed “ring-shaped” area around the milling cutter, whichhinders the incoming of the cutting fluid so that the cutting fluidcannot enter the milling cutter/workpiece interface to cause machiningburns. Therefore, adoption of an appropriate cutting fluid injectionmethod and increase of the proportion of the cutting fluid entering theprocessing area have extremely important effects on boosting the coolingand lubrication effect and improving the surface quality of theworkpiece.

However, at present, there are no good research achievements in theaspect of cutting fluid injection during milling.

SUMMARY OF PRESENT INVENTION

In order to solve the above problems, the disclosure provides a methodand system for milling injected cutting fluid under different workingconditions. In the disclosure, a milling cutter is used to mill aworkpiece, a force measurement instrument is used to measure a millingforce, a cutter change system is used to achieve the change of thecutters, a magazine system is used to achieve the storage of the cuttersand a lubricating system is used to provide lubricating oil to a millinginterface. The position of a nozzle is selected according to airflowfields under different working conditions. The position of the nozzle islocated within an air barrier and in incoming flow, and is not affectedby breaking through the air barrier, thereby saving the useless work ofthe fluid supply system. Meanwhile, the incoming flow can assist thecutting fluid to more efficiently enter the cutting area.

According to some embodiments, the disclosure adopts the followingtechnical solution:

Provided is a method for milling injected cutting fluid under differentworking conditions, comprising the following steps:

analyzing influence of airflow fields in a milling area under differentworking conditions on injection of cutting fluid, quantitativelyanalyzing an influence rule of a helical angle and a rotation speed of acutter on the flow field to determine an optimal target distance of anozzle, an angle between the nozzle and the milling cutter feedingdirection and an angle between the nozzle and the surface of aworkpiece, arranging the nozzle according to a determined settingmanner, and spraying lubricating oil to the milling area by utilizingthe nozzle.

As further definition, when the nozzle is along circumferential flow andin incoming flow, the flow field plays a role in auxiliarytransportation of the injection of the cutting fluid, thereby increasingthe efficiency utilization rate of the cutting fluid.

As further definition, among nozzle position influence factors, thetarget distance can generate the greatest influence, the angle betweenthe nozzle and the milling cutter feeding direction can generate thesecond influence, and the angle between the nozzle and the surface ofthe workpiece can generate the least influence.

As further definition, when the jet flow direction of the nozzle istangent to the flow line of the air flow field, the cutting fluid isinjected along the direction of the airflow, the air flow field plays arole in auxiliary transportation of the injection of the cutting fluid,the angle of the jet flow of the nozzle at this moment is an optimal jetflow angle.

As further definition, the optimal target distance of the nozzle iswithin the air barrier.

As further definition, the optimal position of the nozzle varies withchange in the helical angle and the rotation speed of the millingcutter, the angle between the nozzle and the milling cutter feedingdirection is related to the helical angle of the milling cutter, whenthis angle is the same as the helical angle, it is the most conducive tothe incoming of the cutting fluid; the target distance of the nozzle isrelated to the rotation speed of the milling cutter, and the diameter ofthe milling cutter does not affect the position of the nozzle.

As more further definition, when the rotation speeds of the millingcutter are 600 r/min and 1200 r/min, the maximal value of the targetdistance is within 30 mm; when the rotation speeds of the milling cutterare 1800 r/min and 2400 r/min, the maximal value of the target distanceis within 20 mm.

As further definition, the rotation speed of the milling cutter does notaffect the angle between the nozzle and the milling cutter feedingdirection, but the optimal target distance decreases with increase ofthe rotation speed of the milling cutter.

As further definition, on the basis that the position of the nozzle isensured to be in the incoming flow of the airflow field, improvement ofthe rotation speed of the milling cutter or/and increase of the diameterof the milling cutter can promote the transportation effect of theairflow field on the cutting fluid and improve the effective utilizationrate of the cutting fluid.

Provided is a system for milling injected cutting fluid under differentworking conditions, comprising a lubricating system, a magazine system,a cutter change system, a cutting system and a force measurement system,wherein:

the magazine system comprises a rotatable rotation shaft on which aplurality of cutter assemblies are circumferentially distributed, eachcutter assembly is provided with a mandrel and a cutter connected withthe lower end of the mandrel, the helical angles of various cutters arenot identical, and the cutter adapted to the working conditioncorresponds to the cutter change system through the rotation of therotation shaft;

the cutter change system comprises two mechanical arms whose directionsare opposite, the rotation shaft is arranged in the middle of the twomechanical arms, conversion of the positions of the two mechanical armsis achieved by controlling the rotation of the rotation shaft and thenthe change between the principal axis cutter of the cutting system andthe cutter of the magazine system is realized;

the cutting system comprises the mandrel on which the principal axiscutter is arranged, the rotation of the principal axis cutter is drivenby controlling the rotation of the mandrel, thereby achieve cutting;

the force measurement system is arranged at the lower end of the cuttingsystem, when a cutting forced is applied to a workpiece fixed on theforce measurement system, the cutting force applied to the workpiece ismeasured, and the cutters having different helical angles are selectedfor milling according to processing parameters;

the lubricating system provides lubricating oil for the cutting system,the power source of the lubricating system is a high-pressure gas, theinput frequency and quantity of the high-pressure gas are respectivelycontrolled by a frequency generator and a control valve, the quantity oflubricating oil in a lubricating pump is indirectly adjusted, thelubricating oil provided by the lubricating system is sprayed to themilling area acted by the cutting system respectively through apipeline, a nozzle pipe and a nozzle, and the position of the nozzle isadjusted depending on difference in flow fields of the milling areas andhelical angles and rotation speeds of the cutters under differentworking conditions.

As further definition, the lubricating system comprises a gas inletinterface, a gas source processor, a lubricating pump, a nozzle andconnection pipelines, and control valves are arranged on variousconnection pipelines, the gas inlet interface is fixed on the gas sourceprocessor, the high-pressure gas enters the gas source processor via thegas source processor for filtration to provide the high-pressure gas forthe lubricating system, the gas source processor is connected to asolenoid valve through a dual-direction joint to control the incoming ofthe high-pressure gas, the outlet of the solenoid valve is connectedwith a tee, the high-pressure gas enters the frequency generator via oneoutlet pipeline of the tee, the input frequency of the high-pressure gasis controlled through the frequency generator, the high-pressure gasenters the lubricating pump through the pipeline after coming out of thefrequency generator, and the output joint of the lubricating pump isconnected with the joint of the nozzle to provide the lubricating oilfor the cutting system; the high-pressure gas enters the lubricatingpump through another outlet pipeline of the tee, one end of the joint ofan oil cup is in threaded connection, the other end is in threadedconnection with a lubricating pump fixing cover, the lubricating pumpfixing cover is connected with the lubricating pump, the lubricatingpump fixing cover is fixed on a box body, the quantity of thehigh-pressure gas is adjusted by adjusting a gas quantity adjustmentknob, and the quantity of the lubricating oil is adjusted by adjustingan oil quantity adjustment knob.

As further definition, the force measurement system comprises aworkbench, a workpiece holder and a measurement element, the workbenchis arranged right under the cutting system, the workpiece holder isfixed on the workbench, complete positioning is achieved through theworkpiece holder and the workbench by utilizing the workpiece' ownfreedom, the measurement element collects the cutting force applied tothe workpiece, a measurement signal is amplified by an amplifier to betransferred to an information collection instrument, and then conductedto a computer via a wire to display the cutting force;

the workpiece holder comprises clamping elements in X-Y-Z-axis threedirections, the clamping element in the X-axis direction comprises aplurality of positioning screws, the clamping element in the Y-axisdirection comprises fastening screws and positioning blocks, one face ofthe positioning block contacts with the side of the workpiece, one facecontacts with the screws, and the positioning screw is tightly screwedso that the positioning block is clamped in the X direction of theworkpiece; the clamping element in the Z-axis direction comprises aplurality of pressing plates for clamping, each pressing plate is aself-adjusting pressing plate, and the adjustment of equipment isachieved according to the size of the workpiece through clampingelements in X-Y-Z-axis three directions, thereby meeting the requirementon change in the size of the workpiece.

As compared with the prior art, the disclosure has the beneficialeffects:

The disclosure provides a method for determining the optimal position ofthe nozzle under different working conditions. This position can avoidenergy consumption for breaking through the gas barrier in the processof supplying the cutting fluid, thereby saving the useless work energyof the fluid supply system. At the same time, under the transportationof the pressure and the incoming flow, the cutting fluid can obtain morepower and energy in the airflow field, thereby avoiding the return flowand increasing the flux of the cutting fluid passing through thecutter/workpiece interface.

The discloses provides a milling system which can realize differentworking conditions, and can realize dry milling and milling underworking conditions of pouring lubrication, micro lubrication and nanofluid micro lubrication, and meanwhile different cutters can be selectedaccording to different cutting parameters.

DESCRIPTION OF THE DRAWINGS

The description and drawings constituting one part of this applicationare used to provide further understanding of this application. Theschematic embodiments and descriptions of this application are intendedto explain this application, but not constitute an improper limitationof this application.

FIG. 1 is a shaft side view of a method and experiment system formilling injected cutting fluid under different working conditions.

FIG. 2 is an exploded assembly view of a lubricating system.

FIG. 3 is a shaft side view of a magazine system.

FIG. 4 is a top view of a cutter head.

FIG. 5 is a shaft side view and a front view of a mandrel.

FIG. 6 is a shaft side view of a cutter change system.

FIG. 7 is a shaft side view of a cutting system.

FIG. 8 is a shaft side view of a force measurement system.

FIG. 9 is a diagram showing positioning and clamping of a workpiece.

FIG. 10 is a shaft side view of a milling force measuring instrument.

FIG. 11 is a schematic diagram of nozzle angle 3.

FIG. 12 is a schematic diagram of nozzle angle α.

FIG. 13 is a schematic diagram of surface forces in X and Y directionson an air flow micro element.

FIG. 14 is a schematic diagram of a physical model of a milling airflowfield and an airflow field.

FIG. 15 is a cross-sectional view of a section airflow field of Z=20 mm.

FIG. 16 is a partial enlarged view of a 30° section air flow field.

FIG. 17 is a schematic diagram of a measurement section line.

FIG. 18 is a graph of a Y-direction speed curve on four section lines.

FIG. 19 is a graph of a pressure curve on four section lines.

FIG. 20 is a flow line diagram of an air flow field having a Z=20 mmsection at different rotation speeds.

FIG. 21 is a flow line diagram of an air flow field having a 30° sectionat different rotating speeds.

FIG. 22 is a flowing speed graph of air around a milling cutter atdifferent speeds.

FIG. 23 is a graph of a pressure around a milling cutter at differentspeeds.

FIG. 24 is a flow line diagram of an air flow field having a Z=20 mmsection under milling cutters having different spiral angles.

FIG. 25 is a flow line diagram of an air flow field having an optimaljet angle section under milling cutters having different spiral angles.

FIG. 26 is a flow line diagram of an air flow field having Z=20 mmsection under different milling cutter diameters.

FIG. 27 is a flow line diagram of an air flow field having 30° sectionunder different milling cutter diameters.

Where, lubricating system I, magazine system II, cutter change system m,cutting system IV, force measurement system V, box body I-1, oil cupjoint I-2, oil cup I-3, fastening screw I-4, gasket I-5, fastening screwI-6, lubricating pump fixing cover I-7, precise micro lubricating pumpI-8, gas quantity regulating knob I-9, tee I-10, solenoid valve I-11,gas source processor I-12, gas inlet interface I-13, dual-directionjoint I-14, frequency generator I-15, pipeline I-16, pipeline I-17,pipeline I-18, oil quantity resulting knob I-19, and oil pump outletjoint I-20

Motor case II-1, mandrel II-2, cutter head II-3, and milling cutterII-4.

Motor case III-1, mechanical arm III-2, mechanical arm III-3.

Motor case IV-1, pipeline IV-2, screw IV-3, gasket IV-4, magneticsucking disc IV-5, nozzle interface IV-6, lubricating pump fixing coverIV-7, mandrel IV-8, nozzle IV-9, milling cutter IV-10, workbench IV-1.

Computer V-1, wire V-2, force information collection instrument V-3,amplifier V-4, pressing plate V-5, cylindrical gasket V-6, pressingplate nut V-7, pressing plate screw V-8, workpiece V-9, flat plate screwV-10, small pressing plate screw V-11, positioning screw V-12, workpieceholder V-13, positioning block V-14, dynamometer V-15, screw V-16,holder screw V-17, flat plate V-18, flat plate V-19.

Rear angle II-4-1, rear cutter face II-4-2, front angle II-4-3, chipremoval groove II-4-4, front cutter face II-4-5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The disclosure will be further described in combination with drawingsand embodiments.

It should be noted that the following descriptions are all illustrative,and intended to provide further description for this application. Unlessindicated otherwise, all the technical terms and scientific terms usedin this text have the same meaning as that understood by those ofordinary skill in the art.

It is noted that the terms used herein are only for describing specificembodiments and are not intended to limit exemplary embodimentsaccording to this application. As used herein, the singular is intendedto include the plural, unless the context otherwise expressly indicates.In addition, it is also understood that when the terms “include” and/or“comprise” are used in this description, they indicate that there arefeatures, steps, operations, devices, components and/or theircombinations.

In the disclosure, the orientation or position relationship indicated byterms such as “up”, “down”, “left”, “right”, “front”, “back”,“vertical”, “horizontal”, “side”, “bottom” is the orientation orposition relationship show based on drawings, they are relative termsonly for facilitating description of the structural relationship of eachcomponent or element of the disclosure, but not specifically refer toany one component or element of the disclosure, which cannot beunderstood as a limitation of the present disclosure.

In the disclosure, terms such as “fixed connection”, “linkage” and“connection” should be understood in a broad sense, indicating thatcomponents or elements can be fixedly connected, integrally connected ordetachably connected; directly connected or indirectly connected throughan intermediate medium. For the relevant scientific research ortechnical personnel in the art, the specific meaning of the above termsin the disclosure can be determined according to the specific situation,but cannot be understood as limiting the disclosure.

FIG. 1 is a shaft side view of a method and experiment system formilling cutting fluid under different working conditions.

As shown in FIG. 1, the disclosure comprises five systems, namely, alubricating system I, a magazine system II, a cutter change system III,a cutting system IV and a force measurement system V. The lubricatingsystem I mainly provides milling lubricating oil for cooling andlubricating, the magazine system II realizes storage of cutters, thecutter change system III realizes use of cutters, the cutting system IVis used for milling workpieces, and the force measurement system V ismainly used for measuring a milling force when the workpiece is milled.

FIG. 2 is an exploded assembly view of a lubricating system.

As shown in FIG. 2, the lubricating system includes a box body I-1, anoil cup joint I-2, an oil cup I-3, a fastening screw I-4, gaskets I-5,fastening screws I-6, a lubricating pump fixing cover I-7, a precisemicro lubricating pump I-8, a gas quantity regulating knob I-9, a teeI-10, a solenoid valve I-11, a gas source processor I-12, a gas inletinterface I-13, a dual-direction joint I-14, a frequency generator I-15,a pipeline I-16, a pipeline I-17, a pipeline I-18, an oil quantityresulting knob I-19 and an oil pump outlet joint I-20.

The gas inlet interface I-13 is fixed on the gas source processor I-12,a high-pressure gas enters the gas source processor I-12 via the gasinlet interface I-13 to be filtered to provide the high-pressure gas forthe lubricating system, the gas source processor I-12 is connected tothe solenoid valve I-11 through the dual-direction joint I-14 to controlthe incoming of the gas, the outlet of the solenoid valve I-11 isconnected with a tee I-10, the high-pressure gas enters the frequencygenerator I-15 through one outlet pipeline I-16 of the tee I-10, theinput frequency of the gas is controlled through the frequency generatorI-15, the high-pressure enters the precise micro lubricating pump I-8through the pipeline I-17 after coming out of the frequency generatorI-15; in addition, the high-pressure gas enters the precise microlubricating pump I-8 through another outlet pipeline I-18, one end ofthe oil cup joint I-2 is in threaded connection, the other end is inthreaded connection with the lubricating pump fixing cover I-7, thelubricating pump fixing cover I-7 is connected with the precise microlubricating pump I-8 through two fastening screws I-6, the lubricatingpump fixing cover I-7 is fixed on the box body I-1 through two fasteningscrews I-4 and the gaskets I-5, the quantity of the high-pressure gas isadjusted by adjusting the gas quantity adjustment knob I-9, the quantityof the lubricating oil is adjusted by adjusting the oil quantityadjustment knob I-19, and finally, lubricating oil is provided for thecutting system IV by connecting the oil pump outlet joint I-20 with thenozzle joint IV-6.

FIG. 3 is a shaft side view of a magazine system, FIG. 4 is a side viewof a cutter head, FIG. 5 is a shaft side view and a front view of amandrel, and FIG. 6 is a shaft side view of a cutter change system.

Referring to FIGS. 3-6, the motor case II-1 realizes rotation of thecutter head II-3 through an interior structure and then drives therotation of the mandrel II-2 and the cutter II-4 on the cutter headII-3, the motor case III-1 realizes the position conversion of themechanical arm III-2 and the mechanical arm III-3 through the interiorstructure so as to achieve the change of the processing cutter, therebyrealizing selection of different cutters for processing according todifferent working conditions.

FIG. 7 is a shaft side view of a cutting system. The motor case IV-1realizes rotation of the mandrel IV-8 through the interior structure, sothat the principal axis milling cutter IV-10 rotates and milling isrealized. The lubricating oil provided by the lubricating system I issprayed to the cutting area through the pipeline IV-2, the nozzle pipeIV-7 and the nozzle IV-9. The magnetic sucking disc IV-5 is fixed withthe nozzle joint IV-6 through the screw IV-3 and the gasket IV-4, andthe magnetic sucking disc IV-5 is sucked on the case body of the motorcase IV-1.

FIG. 8 is a shaft side view of a force measurement system, FIG. 9 is agraph showing positioning and clamping of a workpiece, and FIG. 10 is ashaft side view of a force measurement instrument.

Referring to FIGS. 8-10, the force measurement instrument V-15 isfastened on the workbench IV-11 with screws V-16. The workpiece holderV-13 is fixed on the workbench of the force measurement instrument V-15,and the workpiece V-9 is placed on the workbench of the forcemeasurement instrument V-15. The six freedoms degrees of the workpieceV-9 can be fully positioned through the workpiece holder V-13 and theworkbench of the force measurement instrument V-15. Two positioningscrews V-12 used for clamping in the X-axis direction of the workpieceV-9, and the workpiece V-9 is clamped with the workpiece holder screwV-17 in the Y direction of the workpiece. One face of the positioningblock V-14 is in contact with the side of the workpiece V-9 and theother face is in contact with two positioning screws V-12. Thepositioning screw V-12 is screwed so that the positioning block V-14 isclamped in the X direction of the workpiece V-9. The workpiece V-9 isclamped with three pressing plates V-5 in the Z direction. The threepressing plates V-5 constitute a self-adjusting pressing plate by virtueof the flat plate V-18, the flat plate V-19, the cylindrical gasket V-6,the pressing plate screw V-8 and the pressing plate nut V-7. When thelength, width and height of the workpiece V-9 are changed, theadjustment of equipment can be realized by two holder screws V-17, twopositioning screws V-12 and three pressing plates V-5, thereby meetingthe requirement on change in the size of the workpiece V-9. Thepositioning block V-14 is clamped with the small pressing plate screwV-11 and the positioning screw V-12. When the cutting force is appliedto the workpiece V-9, the measurement signal is amplified by theamplifier V-4 and then transmitted to the force information acquisitioninstrument V-3, and finally, the signal is transmitted to the computerV-1 via the wire V-2 and the cutting force is displayed.

FIG. 11 is a schematic diagram of nozzle angle β, and FIG. 12 is aschematic diagram of nozzle angle α.

Referring to FIG. 11 and FIG. 12, in milling, the position of the nozzlehas a very important influence on the cooling and lubricating effect ofthe cutting fluid. Among them, the target distance (h) has the greatestinfluence, then the angle (β) between the nozzle and the milling cutterfeeding direction has the second influence, and the angle (α) betweenthe nozzle and the surface of the workpiece has the least influence. Dueto the effect of the airflow field in milling, the optimal jet flowposition of the nozzle changes with the change in different workingconditions.

FIG. 13 is a schematic diagram of surface forces on the gas flow microelements in the X and Y directions.

Referring to FIG. 13, a rectangular air fluid micro element is selectedon the surface of the milling cutter edge, the air gravity is ignored,and the air can be regarded as incompressible fluid at low speed. Forthe hexahedral micro element, in the x direction, the mass differencebetween input and output at the x and x+dx positions of hexahedronwithin dt time:

$\begin{matrix}{{\left( {\rho \; v_{x}{dydzdt}} \right) - {\left\lbrack {{\rho \; v_{x}} + {\frac{\partial\left( {\rho \; v_{x}} \right)}{\partial x}{dx}}} \right\rbrack {dydzdt}}} = {{- \frac{\partial\left( {\rho \; v_{x}} \right)}{\partial x}}{dxdydzdt}}} & (1)\end{matrix}$

Within the dt time, the mass difference between input and output in thewhole hexahedron:

$\begin{matrix}{{{{- \frac{\partial\left( {\rho \; v_{x}} \right)}{\partial x}}{dxdydzdt}} - {\frac{\partial\left( {\rho \; v_{y}} \right)}{\partial y}{dxdydzdt}} - {\frac{\partial\left( {\rho \; v_{z}} \right)}{\partial z}{dxdydzdt}}} = {{- \left\lbrack {\frac{\partial\left( {\rho \; v_{x}} \right)}{\partial x} + \frac{\partial\left( {\rho \; v_{y}} \right)}{\partial y} + \frac{\partial\left( {\rho \; v_{z}} \right)}{\partial z}} \right\rbrack}{dxdydzdt}}} & (2)\end{matrix}$

The formula of the mass change in the micro element (3):

$\begin{matrix}{\frac{\partial\rho}{\partial t}{dxdydzdt}} & (3)\end{matrix}$

Therefore, a continuous equation represents the formula (4), itsphysical significance is that an algebraic sum of an output and inputmass difference and an interior mass change of fluid flowing through aunit volume space in unit time is zero.

$\begin{matrix}{{\frac{\partial\rho}{\partial t} + \frac{\partial\left( {\rho \; v_{x}} \right)}{\partial x} + \frac{\partial\left( {\rho \; v_{y}} \right)}{\partial y} + \frac{\partial\left( {\rho \; v_{z}} \right)}{\partial z}} = 0} & (4)\end{matrix}$

A vector form is as follows:

$\begin{matrix}{{{\nabla{\cdot \left( {\rho \; \overset{\rightarrow}{v}} \right)}} + \frac{\partial\rho}{\partial t}} = 0} & (5)\end{matrix}$

Continuity equation is one of the most basic differential equations offluid flow. The continuous motion of any fluid must be satisfied.

The differential equation of ideal fluid motion is an importanttheoretical basis for the study of fluid kinematics. It can be deducedby Newton's second law. The positive direction of the x-axis of themicro element is subjected to mass force f_(x)ρdrdydz and surface force

${p - {\frac{\partial p}{\partial x}\frac{dx}{2}}},$

and the negative direction of the x-axis is subject to surface force

$p + {\frac{\partial p}{\partial x}{\frac{dx}{2}.}}$

The motion differential equation in the x axis direction is obtainedaccording to Newton's second law:

$\begin{matrix}{{{f_{x}\rho \; {dxdydz}} + {\left( {p - {\frac{\partial p}{\partial x}\frac{dx}{2}}} \right){dydz}} - {\left( {p + {\frac{\partial p}{\partial x}\frac{dx}{2}}} \right){dydz}}} = {\rho \; {dxdydz}\frac{\; {du}_{x}}{dt}}} & (6)\end{matrix}$

The differential equation of ideal fluid motion, namely, differentialequation of Eulerian motion is:

$\begin{matrix}\left. \left. \begin{matrix}{{f_{x} - {\frac{1}{\rho}\frac{\partial p}{\partial x}}} = \frac{{du}_{x}}{dt}} \\{{f_{y} - {\frac{1}{\rho}\frac{\partial p}{\partial y}}} = \frac{{du}_{y}}{dt}} \\{{f_{z} - {\frac{1}{\rho}\frac{\partial p}{\partial z}}} = \frac{{du}_{z}}{dt}}\end{matrix} \right\}\rightarrow\left\{ \begin{matrix}{{\frac{\partial u_{x}}{\partial t} + {\frac{\partial u_{x}}{\partial x}u_{x}} + {\frac{\partial u_{x}}{\partial y}u_{y}} + {\frac{\partial u_{x}}{\partial z}u_{z}}} = {X - {\frac{1}{\rho}\frac{\partial p}{\partial x}}}} \\{{\frac{\partial u_{y}}{\partial t} + {\frac{\partial u_{y}}{\partial x}u_{x}} + {\frac{\partial u_{y}}{\partial y}u_{y}} + {\frac{\partial u_{y}}{\partial z}u_{z}}} = {Y - {\frac{1}{\rho}\frac{\partial p}{\partial y}}}} \\{{\frac{\partial u_{z}}{\partial t} + {\frac{\partial u_{z}}{\partial x}u_{x}} + {\frac{\partial u_{z}}{\partial y}u_{y}} + {\frac{\partial u_{z}}{\partial z}u_{z}}} = {Z - {\frac{1}{\rho}\frac{\partial p}{\partial z}}}}\end{matrix} \right. \right. & (7)\end{matrix}$

The stress at any point in a viscous flow field has 9 components,including 3 normal stress components and 6 shearing stress components.The total force component of the micro element surface force is furtherderived:

$\begin{matrix}\left\{ \begin{matrix}{{{X\text{:}\; \frac{\partial\sigma_{xx}}{\partial x}{dxdydz}} + {\frac{\partial\tau_{yx}}{\partial y}{dydxdz}} + {\frac{\partial\tau_{zx}}{\partial z}{dzdxdy}}} =} \\{\left( {\frac{\partial\sigma_{xx}}{\partial x} + \frac{\partial\tau_{yx}}{\partial y} + \frac{\partial\tau_{zx}}{\partial z}} \right){dxdydz}} \\{{{Y\text{:}\; \frac{\partial\tau_{xy}}{\partial x}{dxdydz}} + {\frac{\partial\sigma_{yy}}{\partial y}{dydxdz}} + {\frac{\partial\tau_{zy}}{\partial z}{dzdxdy}}} =} \\{\left( {\frac{\partial\tau_{xy}}{\partial x} + \frac{\partial\sigma_{yy}}{\partial y} + \frac{\partial\tau_{zy}}{\partial z}} \right){dxdydz}} \\{{{Z\text{:}\; \frac{\partial\tau_{xz}}{\partial x}{dxdydz}} + {\frac{\partial\tau_{yz}}{\partial y}{dydxdz}} + {\frac{\partial\sigma_{zz}}{\partial z}{dzdxdy}}} =} \\{\left( {\frac{\partial\tau_{xz}}{\partial x} + \frac{\partial\tau_{yz}}{\partial y} + \frac{\partial\sigma_{zz}}{\partial z}} \right){dxdydz}}\end{matrix} \right. & (8)\end{matrix}$

The motion equation represented by stress is as follows:

$\begin{matrix}\left\{ \begin{matrix}{{X\text{:}\mspace{14mu} {\rho \left( {\frac{\partial v_{x}}{\partial t} + {v_{x}\frac{\partial\left( v_{x} \right)}{\partial x}} + {v_{y}\frac{\partial\left( v_{x} \right)}{\partial y}} + {v_{z}\frac{\partial\left( v_{x} \right)}{\partial z}}} \right)}} =} \\{{f_{x}\rho} + \left( {\frac{\partial\sigma_{xx}}{\partial x} + \frac{\partial\tau_{yx}}{\partial y} + \frac{\partial\tau_{zx}}{\partial z}} \right)} \\{{Y\text{:}\mspace{14mu} {\rho \left( {\frac{\partial v_{y}}{\partial t} + {v_{x}\frac{\partial\left( v_{y} \right)}{\partial x}} + {v_{y}\frac{\partial\left( v_{y} \right)}{\partial y}} + {v_{z}\frac{\partial\left( v_{y} \right)}{\partial z}}} \right)}} =} \\{{f_{y}\rho} + \left( {\frac{\partial\tau_{xy}}{\partial x} + \frac{\partial\sigma_{yy}}{\partial y} + \frac{\partial\tau_{zy}}{\partial z}} \right)} \\{{Z\text{:}\mspace{14mu} {\rho \left( {\frac{\partial v_{z}}{\partial t} + {v_{x}\frac{\partial\left( v_{z} \right)}{\partial x}} + {v_{y}\frac{\partial\left( v_{z} \right)}{\partial y}} + {v_{z}\frac{\partial\left( v_{z} \right)}{\partial z}}} \right)}} =} \\{{f_{z}\rho} + \left( {\frac{\partial\tau_{xz}}{\partial x} + \frac{\partial\tau_{yz}}{\partial y} + \frac{\partial\sigma_{zz}}{\partial z}} \right)}\end{matrix} \right. & (9)\end{matrix}$

The above formula is the motion equation of viscous fluid represented bystress, which is applicable to laminar fluid, turbulent fluid, Newtonianfluid and non-Newtonian fluid. In order to specifically describe themotion of fluid, Navier-Stokes equation (N-S equation for short) must beestablished. An equation set is established under constant viscosityaccording to N-S equation:

$\begin{matrix}\left\{ \begin{matrix}{\frac{\partial v_{x}}{dt} = {f_{x} - {\frac{1}{\rho}\frac{\partial p}{\partial x}} + {v\left( {\frac{\partial^{2}v_{x}}{\partial x^{2}} + \frac{\partial^{2}v_{x}}{\partial y^{2}} + \frac{\partial^{2}v_{x}}{\partial z^{2}}} \right)} + {\frac{1}{3}v\; \frac{{\partial\nabla} \cdot \overset{\rightarrow}{v}}{\partial x}}}} \\{\frac{\partial v_{y}}{dt} = {f_{y} - {\frac{1}{\rho}\frac{\partial p}{\partial y}} + {v\left( {\frac{\partial^{2}v_{y}}{\partial x^{2}} + \frac{\partial^{2}v_{y}}{\partial y^{2}} + \frac{\partial^{2}v_{y}}{\partial z^{2}}} \right)} + {\frac{1}{3}v\; \frac{{\partial\nabla} \cdot \overset{\rightarrow}{v}}{\partial y}}}} \\{\frac{\partial v_{z}}{dt} = {f_{z} - {\frac{1}{\rho}\frac{\partial p}{\partial z}} + {v\left( {\frac{\partial^{2}v_{z}}{\partial x^{2}} + \frac{\partial^{2}v_{z}}{\partial y^{2}} + \frac{\partial^{2}v_{z}}{\partial z^{2}}} \right)} + {\frac{1}{3}v\; \frac{{\partial\nabla} \cdot \overset{\rightarrow}{v}}{\partial z}}}}\end{matrix} \right. & (10)\end{matrix}$

The vector form is as follows:

$\begin{matrix}{\frac{d\overset{\rightarrow}{v}}{dt} = {\overset{\rightarrow}{f} - {\frac{1}{\rho}{\nabla p}} + {v{\nabla^{2}\overset{\rightarrow}{v}}} + {\frac{1}{3}v{\nabla\left( {\nabla{\cdot \overset{\rightarrow}{v}}} \right)}}}} & (11)\end{matrix}$

A flow function and a vorticity equation are seen in formulas 12 and 13.

$\begin{matrix}{{\frac{\partial^{2}\psi}{\partial x^{2}} + \frac{\partial^{2}\psi}{\partial y^{2}}} = {- \Omega}} & (12) \\{{\frac{\partial\Omega}{\partial t} + {\frac{\partial\psi}{\partial y}\frac{\partial\Omega}{\partial x}} - {\frac{\partial\psi}{\partial x}\frac{\partial\Omega}{\partial y}}} = {\gamma \left( {\frac{\partial^{2}\Omega}{\partial x^{2}} + \frac{\partial^{2}\Omega}{\partial y^{2}}} \right)}} & (13)\end{matrix}$

Further, boundary conditions are selected according to solved problems.The flow function values of all nodes in the whole flow field can beobtained by using the iterative method.

FIG. 14 is a physical model of a milling airflow field and a schematicdiagram of an airflow field.

Referring to FIG. 14, in high-speed milling, the spindle drives thecutter to rotate at high speed, rotation motion can can disturb thesurrounding air and create an air boundary layer around the millingcutter to hinder the cutting fluid to enter the processing area. Thehandle part of the milling cutter is cylindrical, and the formed airflow is circumferential flow. The cutting-edge part has a milling cuttergroove, and revolving air flow along the direction of the cutter grooveis formed. The circumferential flow and the revolving air flow areinfluenced from each other, which has an inhibition effect on the supplyof cutting fluid.

Therefore, the distribution of the airflow field around the rotarymilling cutter is simulated by using FLUENT software. The modelconditions are as follows: milling cutter diameter r=20 mm, millingcutter helical angle β=300, rotation speed n=1200 r/min, the millingcutter is in a static airflow field, and simulation parameters are shownin table 1.

TABLE 1 Simulation parameters of flow field of rotary milling cutterName Sizes Diameter of milling 20 cuter (mm) Helical angle (°) 30Rotation speed of 1200 milling cutter (r/min) Diameter of flow field 150(mm)

A 3D solver is used to calculate the simulation. The air is selected asa flow medium, a flow field outlet boundary is set as a pressure outletboundary, namely, pressure-outlet boundary, the boundary condition ofthe workpiece is set as a static wall, the boundary condition of themilling cutter is set as a rotating wall, the boundary conditions areinitialized, and solution is performed after residual monitoring is set.After a certain number of iterations, the calculation results areobtained after convergence.

FIG. 15 is an airflow field screenshot having a Z=20 mm section.

Referring to FIG. 15, airflow formed by a rotary milling cutter in thecircumferential direction is called the circumferential flow. It can beseen that the circumferential flow is spiral, the feed direction of themilling cutter is in the negative direction of the Y axis, the jet flowof the nozzle is toward the milling cutter tip, and when the jet flowdirection is tangent to the flow line of the air flow field, the cuttingfluid is injected along the airflow direction, the air flow field canplay a role in auxiliary transportation of the injection of cuttingfluid so as to transport more cutting fluid to the surface of thecutter/workpiece, and therefore the jet flow angle of the nozzle at thismoment is the optimal jet flow angle, the jet flow and the millingcutter feeding direction are angled at 30°.

FIG. 16 is a partial enlarged view of an air flow field having a 30°section.

Referring to FIG. 16, the angle and distance between the jet flow andthe horizontal direction also affect the injection of the cutting fluid,and therefore the sectional airflow field is further analyzed when thejet flow and the milling cutter feeding direction are angled at 30°. Itcan be seen that various air flows around the milling area aredistributed. The outermost layer is the air barrier which hinders thecutting fluid to enter the cutting area, and therefore there is a needto avoid the position of the jet flow to be beyond the air barrier. Theincoming flow is airflow whose direction is directed to the surface ofthe milling cutter, which is beneficial to entering of the cuttingfluid, the cutting fluid reaches the periphery of the milling cutter andthe milling cutter groove along with the incoming air flow so as to takethe effect of transporting the cutting fluid. One portion of cuttingfluid is adhered to the surface of the workpiece to form a layer oflubricating oil film so as to take the effects of reducing abrasion andresisting abrasion and cooling the lubricating cutter/workpieceinterface. One portion of cutting fluid flows out along with “returnflow”, the “return flow” is air flow whose direction is opposite to thesurface of the milling cutter, the existence of “return flow” makespartial cutting fluid flow out of the cutting area and meanwhile plays arole in inhibiting the cutting fluid to enter the cutting area, andtherefore it should be avoided that the injection of the cutting fluidis in contact with “return flow”. The optimal injection angle anddistance of the cutting fluid are as shown in the drawings. According tomeasurement, when the nozzle jet flow direction and the cutter feedingdirection are angled at 30° and when the axis of the nozzle and thesurface of the workpiece are at a certain angle (40°-50°) and in acertain distance (20-30 mm), the airflow field can play a role intransporting the cutting fluid, and meanwhile “return flow” can hinderthe cutting fluid to the smallest extent so that the cutting fluid moreeasily enters the cutting area, thereby presenting the maximallubricating and cooling effects.

FIG. 17 is a diagram of a measurement section line.

Referring to FIG. 17, in order to quantitatively study the position ofreturn flow and the thickness of radial flow in the milling flow field,on a section which is at 30° from the milling cutter feeding direction,measurement is carried out on four measurement sections with differentdistances from the center of the milling cutter in the milling flowfield. The four measurement sections are distanced from the center ofthe milling cutter by L1=12 mm, L2=15 mm, L3=20 mm and L4=25 mmrespectively.

FIG. 18 is a speed curve graph in the Y direction on four section lines,and FIG. 19 is a graph of a pressure curve on four section lines.

Referring to FIGS. 18 and 19, according to analysis, on the 30° section,when the speed in the Y direction is negative, the speed directionpoints to the milling cutter, which represents that the air flow flowstoward the milling cutter at this moment and is the incoming flow; andwhen the speed in the Y direction is positive, which represents that theair flow flows out of the milling cutter at this moment and is thereturn flow. The size of X axis represents the distance from the surfaceof the workpiece, and the larger the X is, the farther it is from thesurface of the workpiece. On the section line of L=12 mm, when x is 0-4mm, the speed in the Y direction is negative, and there is no returnflow, but when x=4-4.5 mm, the speed in the Y direction is positive, andthe return flow appears. When x>4.5 mm, the return flow disappearsagain, which means that the return flow appears at L=12 mm, thethickness of the radial flow is 2 mm, and the speed of the air flow isthe largest. On the section line of L=15 mm, when x<5 mm, the speed ispositive, and the air flow is return flow at this moment. When x>5 mm,the speed is negative, and the air flow is incoming flow. On the sectionlines of L=20 mm and 25 mm, when the target distance of return flow isx=0˜7 mm, when x>7 mm, the air flow is the incoming flow, and thefarther the distance from the milling cutter, the smaller the speed ofthe return flow is. Further, the distribution of pressures around themilling cutter is analyzed. The pressure curve on the four section linesis as shown in FIG. 19. On the three section lines from the millingcutter by 2 mm, 5 mm and 10 mm, the air pressure is negative, and thecloser the milling cutter is, the smaller the pressure is, and theminimum pressure is in the milling groove. On the section line from themilling cutter by 15 mm, the air pressure is positive. Under the effectof the pressure difference, the air more easily enters the millingcutter/workpiece surface.

FIG. 20 is a flow line diagram of an air flow field having a Z=20 mmsection at different rotation speeds.

FIG. 21 is a flow line diagram of an air flow field having a 30° sectionat different rotation speeds.

Referring to FIGS. 20 and 21, the rotation speed of the cutter canaffect the air flow field in the milling area. Therefore, under thecondition that the diameter, helical angle and other parameters of thecutter are kept constant, the rotation speed of the cutter is changed to600 r/min, 1200 r/min, 1800 r/min and 2400 r/min respectively, and thechange of the air flow field is observed. It can be seen that therotation speed does not affect the shape of the air flow field in thecircumferential direction, so the rotation speed of the milling cutterdoes not affect the angle between the nozzle and the milling cutterfeeding direction, and it is most conducive to the injection of cuttingfluid when they are 30°. According to FIG. 21, it can be seen that thesize of the incoming flow decreases with the increase of the rotationspeed of the milling cutter, while the size of the air barrier graduallyincreases, indicating that the increase of the rotation speed of themilling cutter can increase the difficulty of the cutting fluid enteringthe milling cutter/workpiece interface. At the same time, the optimaldistance of the nozzle should be within the air barrier, and thereforethe optimal target distance can decrease with the increase of therotation speed of the milling cutter. As can be seen from the drawings,when the rotation speed of the milling cutter are 600 r/min and 1200r/min, the maximum target distance should be within 30 mm. When therotation speeds of the milling cutter are 1800 r/min and 2400 r/min, themaximum target distance should be within 20 mm. Further, the rotationspeed of the milling cutter does not affect the angle between the nozzleand the surface of the workpiece, that is, 40°-50° is the most favorablefor the transportation of cutting fluid to the milling cutter/workpieceinterface.

FIG. 22 is a graph of an air flow velocity around a milling cutter atdifferent speeds. FIG. 23 is a graph of a pressure around a millingcutter at different speeds.

Referring to FIGS. 22 and 23, in order to quantitatively analyze theinfluence rule of the rotation speed on the speed of the air flow fieldaround the milling cutter, the air flowing speeds and pressures aroundthe milling cutter at different rotation speeds are respectivelycollected, and air flowing speed and pressure diagrams around themilling cutter at different rotation speeds are established. Thehorizontal coordinate is a length from the surface of the workpiece. Itcan be seen from the drawing that the air flowing speed changesperiodically with the distance from the surface of the workpiece. Theair flowing speeds on the surface of the milling cutter and at the chipdischarge groove are different. When the distance from the surface ofthe workpiece is 30-40 mm, the air flowing speed is the smallest.According to the conservation principle of mechanical energy ofBernoulli fluid: if the speed is small, the pressure is large. The airflow enters the narrow milling groove from the periphery of the millingcutter, the pressure increases and the air flowing speed decreases.Among them, the air flowing speed around the surface of the millingcutter is relatively large, the air flowing speeds can respectivelyreach 0.62 m/s (n=600 r/min), 1.19 m/s (n=1200 r/min), 1.85 m/s (n=1800r/min) and 2.49 m/s (n=2400 r/min). It can be seen that with theincrease of the rotation speed, the influence of the milling cutter onthe airflow field speed around the milling cutter becomes more and moreobvious. The airflow field speed around the milling cutter linearlyincreases with the rotation speed of the milling cutter. It means that,the improvement of the rotation speed can continuously expand the radiusof the air barrier around the milling cutter, increase the difficulty ofthe cutting fluid reaching the interface of milling cutter/chip andmilling cutter/workpiece interface, and reduce the cooling andlubricating effect.

It can be seen from FIG. 23 that the air pressures around the millingcutter are all negative pressures, and the negative pressure increaseswith the increase of the rotation speed of the milling cutter, and theirmaximum values can reach −0.015 Pa (n=600 r/min), −0.035 Pa (n=1200r/min), −0.062 Pa (n=1800 r/min), −0.089 Pa (n=2400 r/min). With theincrease of the negative pressure around the milling cutter, thepressure difference of the incoming flow increases, which is moreconducive to the cutting fluid reaching the radial flow along with theincoming flow and then further being transported to the millingcutter/workpiece interface. Therefore, when the position of the nozzleis in the incoming flow field, with the increase of the rotation speedof the milling cutter, the more obvious the effect of the airflow fieldon the transportation of the cutting fluid is, the higher the effectiveutilization rate of the cutting fluid is.

FIG. 24 is a flow line diagram of an airflow field having a Z=20 mmsection under milling cutters having different spiral angles. FIG. 25 isa flow line diagram of an airflow field having an optimal jet flow anglesection under milling cutters having different spiral angles.

Referring to FIG. 24 and FIG. 25, the helical angle of the millingcutter can also affect the air flow field in the milling area.Therefore, under the condition that the diameter, the rotation speed andother parameters of the cutter are kept unchanged, the helical angles ofthe milling cutter are changed to 30°, 35°, 40° and 45° respectively,and the change of airflow field is observed. It can be seen that thedirection of the circumferential flow varies with the change of thehelical angle of the milling cutter, that is, the optimal angle betweenthe nozzle and the milling cutter feeding direction changes. It can beseen from the drawing that when the angle between the nozzle and themilling cutter feeding direction is the same as the helical angle of themilling cutter, the air flow field can assist in the transportation ofthe cutting fluid, which is conducive to injecting the cutting fluidinto the milling cutter/workpiece interface and increasing the effectiveutilization rate of the cutting fluid. According to FIG. 25, it can beseen that when the angle between the nozzle and the milling cutterfeeding direction is the same as the helical angle, the air flow fieldsformed by the milling cutter rotating at different helical angles havelittle difference. According to the measurement, the optimal targetdistance should be within 20 mm, and the optimal angle between thenozzle and the surface of the workpiece is the same, when they are both40°-50°, it is most conducive to the transportation of the cuttingfluid, so as to achieve the high utilization rate of the cutting fluid.

FIG. 26 is a flow line diagram of an air flow field having Z=20 mmsection under different milling cutter diameters. FIG. 27 is a flow linediagram of an air flow field having 30° section under different millingcutter diameters.

Referring to FIGS. 26-27, the diameter of the milling cutter can alsoaffect the air flow field in the milling area. Therefore, under thecondition that the helical angle, rotation speed and other parameters ofthe milling cutter are kept unchanged, the diameter of the millingcutter is changed respectively to 12 mm, 16 mm, 20 mm and 24 mm, and theinfluence of the diameter of the milling cutter on the airflow field isobserved. In order to quantitatively analyze the influence rule of thediameter of the milling cutter on the constraint interface of the endface milling cutter, the air flowing speeds and pressures around themilling cutters having different diameters are respectively collected,and graphs of air flowing speeds and pressures around the millingcutters having different diameters are established. It can be seen thatthe air flowing speed around the milling cutter increases with theincrease of the diameter of the milling cutter, wherein, the air flowingspeeds are respectively 0.62 m/s (R=12 mm), 0.91 m/s (R=16 mm), 1.22 m/s(R=20 mm) and 1.49 m/s (R=24 mm). This is mainly because the diameter ofthe cutter is increased to result in increase of the linear speed on thesurface of the cutter, the milling cutter drives the increase of the airflowing speed around the milling cutter. When the distance from thesurface of the workpiece is 20-35 mm, the air flow speed decreases andis the lowest, this is because it is located in the chip chute at thismoment, the pressure increases after the air flow enters the narrow chipchute, according to Bernoulli's conservation principle of fluidmechanical energy, the pressure increases and the speed decreases.Change in pressures is further observed. It can be seen that thepressures around the milling cutter are negative, and the negativepressure increases as the diameter increases, and the maximum negativepressure value can reach −0.032 Pa (R=12 mm), −0.026 Pa (R=16 mm),−0.016 Pa (R=20 mm), −0.003 Pa (R=24 mm), respectively. With theincrease of the negative pressure around the milling cutter, thepressure difference of the incoming flow increases, which is moreconducive to the cutting fluid reaching the radial flow along with theincoming flow and then further being transported to the millingcutter/workpiece interface. Therefore, when it is ensured that theposition of the nozzle is in the incoming flow field, the airflow fieldhas a more obvious effect on the transportation of the cutting fluid ismore obvious as the diameter of the milling cutter increases.

To sum up, the position of the nozzle is set by analyzing the flow fieldin the milling area. Under the constraint conditions of the end facemilling cutter, the airflow field around the rotary milling cuttermainly includes the circumferential flow, the incoming flow, the radialflow, the return flow and the air barrier layer. According to thecomplex flow field around the rotary milling cutter, the optimalposition (the angle between the nozzle and the milling cutter feedingdirection, and the angle and target distance between the nozzle and thesurface of the workpiece) of the nozzle can be determined. When thenozzle is along circumferential flow and in the incoming flow, the flowfield can play a role in auxiliary transportation of the injection ofthe cutting fluid, thereby increasing the effective utilization rate ofthe cutting fluid.

The optimal position of the nozzle varies with the change of the helicalangle and rotation speed of the milling cutter. The angle between thenozzle and the milling cutter feeding direction is related to thehelical angle of the milling cutter. When this angle is the same as thehelical angle, it is most conducive to the incoming of the cuttingfluid. The target distance of the nozzle is related to the rotationspeed of the milling cutter. The diameter of the milling cutter does notaffect the position of the nozzle. When the rotation speeds of themilling cutter are 600 r/min and 1200 r/min, the optimal target distanceis 30 mm. When the rotation speeds of the milling cutter are 1800 r/minand 2400 r/min, the optimal target distance is 20 mm, the angle betweenthe nozzle and the surface of the workpiece does not change, and theeffect is best when this angle is 40°-50°.

The above descriptions are only preferred embodiments of thisapplication but are not intended to limit this application. For thoseskilled in the art, various variations and changes can be made to thisapplication. Any modifications, equivalent replacements, improvementsand the like made within the spirit and principle of this applicationshould be included in the scope of protection of this application.

Although embodiments of the disclosure are described in combination withaccompanying drawings, the scope of protection of the disclosure is notlimited. Those skilled in the art that should understand that on thebasis of the technical solution of the disclosure, various modificationsor deformations made by those skilled in the art without any creativeefforts still fall within the scope of protection of the disclosure.

We claim:
 1. A method for milling injected cutting fluid under differentworking conditions, comprising the following steps: analyzing influenceof airflow fields in a milling area under different working conditionson injection of cutting fluid, quantitatively analyzing an influencerule of a helical angle and a rotation speed of a cutter on the flowfield, comprehensively determining an optimal target distance of anozzle, an angle between the nozzle and a milling cutter feedingdirection and an angle between the nozzle and the surface of aworkpiece, setting the nozzle according to a determined setting manner,and spraying lubricating oil to the milling area by utilizing thenozzle.
 2. The method for milling injected cutting fluid under differentworking conditions according to claim 1, wherein when the nozzle isalong circumferential flow and in incoming flow, the flow field plays arole in auxiliary transportation of the injection of the cutting fluid,thereby increasing the efficiency utilization rate of the cutting fluid.3. The method for milling injected cutting fluid under different workingconditions according to claim 1, wherein when the jet flow direction ofthe nozzle is tangent to the flow line of the air flow field, thecutting fluid is injected along the direction of the airflow, the airflow field plays a role in auxiliary transportation of the injection ofthe cutting fluid, the angle of the jet flow of the nozzle at thismoment is an optimal jet flow angle.
 4. The method for milling injectedcutting fluid under different working conditions according to claim 1,wherein the optimal nozzle position varies with change in the helicalangle and the rotation speed of the milling cutter, the angle betweenthe nozzle and the milling cutter feeding direction is related to thehelical angle of the milling cutter, when this angle is the same as thehelical angle, the incoming of the cutting fluid is the most favorable;the target distance of the nozzle is related to the rotation speed ofthe milling cutter, and the diameter of the milling cutter does notaffect the position of the nozzle.
 5. The method for milling injectedcutting fluid under different working conditions according to claim 4,wherein the optimal target distance of the nozzle is within the airbarrier.
 6. The method for milling injected cutting fluid underdifferent working conditions according to claim 5, wherein when therotation speeds of the milling cutter are 600 r/min and 1200 r/min, themaximal value of the target distance is within 30 mm; when the rotationspeeds of the milling cutter are 1800 r/min and 2400 r/min, the maximalvalue of the target distance is within 20 mm.
 7. The method for millinginjected cutting fluid under different working conditions according toclaim 1, wherein on the basis that the position of the nozzle is ensuredto be in the incoming flow of the airflow field, improvement of therotation speed of the milling cutter or/and increase of the diameter ofthe milling cutter can promote the transportation effect of the airflowfield on the cutting fluid and improve the effective utilization rate ofthe cutting fluid.
 8. A system for milling injected cutting fluid underdifferent working conditions, comprising a lubricating system, amagazine system, a cutter change system, a cutting system and a forcemeasurement system, wherein: the magazine system comprises a rotatablerotation shaft on which a plurality of cutter assemblies arecircumferentially distributed, each cutter assembly is provided with amandrel and a cutter connected with the lower end of the mandrel, thehelical angles of various cutters are not identical, and the cutteradapted to the working condition corresponds to the cutter change systemthrough the rotation of the rotation shaft; the cutter change systemcomprises two mechanical arms whose directions are opposite, therotation shaft is arranged in the middle of the two mechanical arms,conversion of the positions of the two mechanical arms is achieved bycontrolling the rotation of the rotation shaft, and then the changebetween the principal axis cutter of the cutting system and the cutterof the magazine system is realized; the cutting system comprises themandrel on which the principal axis cutter is arranged, the rotation ofthe principal axis cutter is driven by controlling the rotation of themandrel, thereby achieving cutting; the force measurement system isarranged at the lower end of the cutting system, when a cutting force isapplied to a workpiece fixed on the force measurement system, thecutting force applied to the workpiece is measured, and the cuttershaving different helical angles are selected for milling according toprocessing parameters; the lubricating system provides lubricating oilto the cutting system, the power source of the lubricating system is ahigh-pressure gas, the input frequency and quantity of the high-pressuregas are respectively controlled by a frequency generator and a controlvalve, the quantity of lubricating oil in a lubricating pump isindirectly adjusted, the lubricating oil provided by the lubricatingsystem is sprayed to the milling area acted by the cutting systemrespectively through a pipeline, a nozzle pipe and a nozzle, theposition of the nozzle is adjusted depending on difference in flowfields of the milling areas and helical angles and rotation speeds ofthe cutters under different working conditions.
 9. The system formilling injected cutting fluid under different working conditionsaccording to claim 8, wherein the lubricating system comprises a gasinlet interface, a gas source processor, a lubricating pump, a nozzleand connection pipelines as well as control valves arranged at variousconnection pipelines, the gas inlet interface is fixed on the gas sourceprocessor, the high-pressure gas enters the gas source processor via thegas source processor for filtration to provide the high-pressure gas forthe lubricating system, the gas source processor is connected to asolenoid valve through a dual-direction joint to control the incoming ofthe high-pressure gas, the outlet of the solenoid valve is connectedwith a tee, the high-pressure gas enters the frequency generator via oneoutlet pipeline of the tee, the input frequency of the high-pressure gasis controlled through the frequency generator, the high-pressure gasenters the lubricating pump through the pipeline after coming out of thefrequency generator, and the output joint of the lubricating pump isconnected with the joint of the nozzle to provide the lubricating oilfor the cutting system; the high-pressure gas enters the lubricatingpump through another outlet pipeline of the tee, one end of the joint ofan oil cup is in threaded connection, the other end is in threadedconnection with a lubricating pump fixing cover, the lubricating pumpfixing cover is connected with the lubricating pump, the lubricatingpump fixing cover is fixed on a box body, the quantity of thehigh-pressure gas is adjusted by adjusting a gas quantity adjustmentknob, and the quantity of the lubricating oil is adjusted by adjustingan oil quantity adjustment knob.
 10. The system for milling injectedcutting fluid under different working conditions according to claim 8,wherein the force measurement system comprises a workbench, a workpieceholder and a measurement element, the workbench is arranged right underthe cutting system, the workpiece holder is fixed on the workbench,complete positioning is achieved through the workpiece holder and theworkbench by utilizing the workpiece' own freedom, the measurementelement collects the cutting force applied to the workpiece, and ameasurement signal is amplified by an amplifier to be transferred to aninformation collection instrument, and then conducted to a computer viaa wire to display the cutting force; the workpiece holder comprisesclamping elements in X-Y-Z-axis three directions, the clamping elementin the X-axis direction comprises a plurality of positioning screws, theclamping element in the Y-axis direction comprises fastening screws andpositioning blocks, one face of the positioning block contacts with theside of the workpiece, the other face contacts with the positioningscrew, and the positioning screw is tightly screwed so that thepositioning block is clamped in the X direction of the workpiece; theclamping element in the Z-axis direction comprises a plurality ofpressing plates for clamping, each pressing plate is a self-adjustingpressing plate, and the adjustment of equipment is achieved according tothe size of the workpiece through clamping elements in X-Y-Z-axis threedirections, thereby meeting the requirement on change in size of theworkpiece.